Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 151218 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 718 AM EST Thu Feb 15 2018 .SYNOPSIS... A broad area of high pressure aloft will remain over the Gulf of Mexico for the next several days. Meanwhile, a series of storm systems will track from west to east across the central and northern parts of the U.S. keeping an active weather pattern in place for much of the region well into next week. One such system will affect the area today into Friday, another over the weekend, and a couple more slated for next week, each bringing widespread precipitation, mostly rain, to the area. Temperatures will be well above normal much of the period with the exception of the weekend when a surge of Canadian air will pass through the area. && .NEAR TERM /THROUGH TONIGHT/... As of 430 AM EST Thursday... A series of fairly vigorous upper-level disturbances in an active zonal flow will remain the dominant pattern well into next week. A broad subtropical ridge currently centered across the Gulf of Mexico, will drift slowly east by early next week to just off the FL/GA/SC east coast. This will for force the upstream disturbances to track around, up and over the blocking western Atlantic ridge setting up a long lasting baroclinic zone over or just to the west of the Mid- Atlantic/central Appalachians/TN- OH Valley region. As a result our region can expect an active wet weather pattern to continue for some time. The main concern will continue to be hydro- related with excessive rain runoff into area creeks, streams, and rivers. However, at the moment, not any one system by itself appears to be enough to trigger significant flooding, at least none of them through the weekend. Early this morning a disturbance was tracking from west to east across the area, taking an area of rain and isolated thunderstorms which moved through our area early last night off the east coast. The next upstream disturbance was evident With the upper ridge to our south beginning to amplify across the southeast U.S. over the next few days, the next upstream disturbance aloft was taking shape across the upper Midwest with a subsequent deepening northern stream trough moving southeast from central Canada. These two systems will combine Friday allowing a frontal system to develop and being to move toward our area. For today, current thinking is that precipitation will be limited primarily to northern parts of the CWA, mainly I-64 corridor and northward as the upper ridge builds and the main baroclinic zone shifts further north into IN/OH/PA. HIRES Models are in good agreement on this keeping likely and greater pops confined to the far northern/northwestern parts of the CWA, with the best chance for significant rainfall really further north toward the PA/MD/northern WV area. However, will be considerable cloud cover and areas of fog and drizzle early this morning, especially westof I-77 and toward the I-64 corridor. Temperatures are well above freezing this morning, so no concerns for winter precipitation. As the aforementioned upper-level systems and front begin to move southeast overnight/early Friday, rain will be on the increase overnight into early Friday, mainly western and northern areas. Temperatures will be well above normal this period as +12 to +14C air at 850mb has overspread the region and will continue in place until the cold front moves it south and east of us later on Saturday. Temperatures early this morning were 20-25F degrees above normal and 20-25F above those observed the past few mornings. No concerns with winter precipitation today or tonight! && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 300 AM EST Thursday... The cold front will move through the region on Friday. The showers will be most pronounced west of the Blue Ridge with the mountains disrupting the precipitation for a bit before some convective instability east of the Ridge can reinvigorate the showers east of the Ridge. There may be a window for thunder as guidance shows some shallow instability in the boundary layer in the afternoon, but confidence in this is not high. While the most vigorous low level winds will be out ahead of the front, there still looks to be a good amount of wind behind the front with a temperature profile that is favorable for mixing in the boundary layer so expect gusty winds to continue through the afternoon. Any lingering showers will be on the decline through Friday night. However, by Saturday morning the next system will be approaching the region from the southwest. Significant upper level jet dynamics will combine with short wave energy and isentropic lift running over the top of a high pressure wedge to generate widespread precipitation. However, there remains a good amount of uncertainty as to exactly how this system will evolve, which will have significant implications for ptype and where the heaviest precipitation will fall. A solution that is farther north will be warmer and likely result in more freezing rain. A solution that is further south, the trend currently favored by the latest model runs, will be colder and favor more snow/sleet and less in the way of freezing rain. At this time, will shade ptype toward more snow/sleet with reduced accumulations due a mixed ptype. This will result in snow/sleet accumulations of an inch or two mainly north of route 460, along with a patchy glaze of ice from freezing rain. Due to the uncertainty, expect this forecast to change as newer guidance becomes available. As the system pulls away Saturday night, upslope showers will linger west of the Blue Ridge with a gradual mix/change to snow with some additional light accumulation possible. We get a brief break in the action on Sunday as high pressure moves in from the west and forms a wedge east of the Appalachains, but a warm front will push some showers back into the area late Sunday night. After a warm start, temperatures will trend colder behind the front on Friday, then be a bit below normal in the wedge on Saturday, followed by a return to near normal readings for Sunday. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 250 PM EST Wednesday... A warm front will track over the wedge bringing another round of precipitation to the region Monday. Temperatures may be warm enough for an all rain event, but there is a small window for a wintry mix Monday morning. The warm front will remove the shallow wedge by Tuesday. The area will stay in the warm sector Tuesday and Wednesday with well above normal temperatures with readings in the 60s. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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As of 705 AM EST Thursday... Weak upper disturbance and warm front moved north and east of the area overnight, respectively, taken the bulk of synoptic- based rainfall with it for now. Light drizzle and areas of fog have developed mainly west of the Blue Ridge. Ceilings are largely MVFR to IFR. The forecast area is now solidly within the warm sector. Temperatures are already in the 50s and 60s this morning and expected to be well above normal today in the 60s west to 70s Piedmont. Clouds will linger, especially through the morning, mostly in the MVFR range, with potential for IFR a few more hours at KBLF. Some breaks in the clouds will be possible during the mid to late afternoon into the early evening before ceilings lower into back into the MVFR range or potentially worse in the west for the remainder of the night. Light rain will begin to spread into western areas late and a sprinkle is possible throughout much of the TAF valid period at all TAF sites. Visibilities will be MVFR or better throughout the TAF valid period with restrictions limited to light BR and occasionally -RA. Winds are expected to remain mostly SW to WSW through the TAF valid period at speeds of 8-12 mph with low end gusts possible at most stations throughout the period with increasingly strong winds aloft. Appears sub-VFR cigs will persist western sections Thursday night with possible VFR returning out east well in advance of the next upstream cold front. Appears most showers as well will hold off overnight except for the KBLF-KLWB corridor where spotty late night coverage appears possible. Extended Aviation Discussion... Deteriorating aviation conditions expected on Friday with a cold front moving slowly through the CWA resulting in widespread MVFR to IFR ceilings and visibilities as light rain increases and spreads across the forecast area. Behind the front going into late Friday and Saturday, strong northwest winds will develop as colder air rushes back in. Conditions look to briefly improve Friday night as high pressure builds in behind the front before another disturbance arrives from the southwest Saturday afternoon/evening. This feature looks to bring another round of sub-VFR cigs/vsbys in rain or mixed precipitation before VFR returns again on Sunday under weak high pressure. The cold/wintry weather will be brief as a warm front lifts back north into the area on Monday with another round of sub- VFR, especially western areas and mountains.
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&& .CLIMATE...
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As of 700 AM EST Thursday... Thursday 02/15/2018 Site MaxT Year HiMin Year KBLF 72 1990 54 1990 KDAN 76 1990 57 1949 KLYH 77 1989 55 1949 KROA 79 1989 55 2001 KRNK 66 1990 46 1990
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...MBS LONG TERM...MBS/RCS AVIATION...RAB CLIMATE...KK

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